This disclosure generally relates to a hydraulic control unit for regulating fluid flow. More particularly, this disclosure relates to a hydraulic control unit for controlling an output pressure provided by at least two pumps.
Positive displacement pumps are utilized to satisfy the high pressure flow demands of a variety of flow applications, including fuel, lubrication and hydraulic actuation systems. Such systems require a large pump capable of providing sufficient fluid flow for the highest demand levels. Moreover, many such systems require variable pressure setting capabilities. However, most operating conditions do not require the highest level of fluid flow. Therefore much of the fluid is simply bypassed to the pump supply or reservoir. Operating a pump at such high bypass levels is inefficient and generates waste heat. The thermal problem is further exacerbated when a high pressure is set. An alternate solution is to utilize a relatively small primary pump, capable of providing pressure and flow associated with low and normal operational demands, in concert with a secondary pump engaged when higher flows are required. Such a multi-pump system introduces additional control challenges. Pressure rise through the secondary pump(s) must be minimized, while still providing a smooth and quick transient response to suddenly increased pressure and flow demand.